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Topic: CR750 replica build (Read 19895 times)

Rob - it certainly did amazing sound Yes they do look a little home-cast!

Phil - your rep is a lovely bike and you have done it remarkably quickly, its great that we have all met through these builds and have managed to help one another. Thanks Phil with a bit of luck it will turn out alright!

I have a week off soon and the plan is to focus on the rolling chassis to progress that along so that I can properly start the dry build.

Hopefully I can kick some life back into this thread!

Oil catch tank:

A little progress on the oil catch tank, this is located underneath the seat of the works CR750.

This is the type of tank I will be replicating:

Thanks to Eric for the info!

Modelled up in CAD a while ago:

I ran a 3D print off in a draft resin (quick and cheap! around 2 hrs build time) to check fitment and clearances before fabricating in Aluminium. As the part is going to be made from thin aluminium I thickened the walls for the 3D print and split it into to pieces, for ease of printing:

I have seen a few different types of tanks, so will do a little more research before starting!

The oil catch tank or 'Sniffer box' as some people call it, is quite the point of controversy across forums!

The one that I drew up and 3D printed was a copy of a copy. This was created over in France by a chap who has built a few replicas, however it does not seem to be as accurate as I originally thought. Another CR guru (thanks if you are reading!) has steered me towards a more correct design, based on some old images and notes from the factory bikes.

It looks a little different now!

Ref image 1

Ref image 2

Apparently two versions of this tank were available.

The side breather/exhaust was apparently what was at Daytona and on the works bikes. I imagine this was to do with the short seat.

And the rear breather on the kit bikes:

As I am creating a CR works style bike replicating the Daytona winning bike, I will be going for the side exit catch tank variant. I will probably make up a 'buck' to create the radii on the edges, and roll a piece in the centre to match, then spring bend the inlet/outlets. The original notes show some baffles as well so it would be good to build these in.

It is so difficult with these bikes to be 'accurate' as the bikes that were at Daytona were all slightly different, the 'kit' bikes had a variety superseded parts across the years and of course there are a few replicas out there.

- And finally the rear hub: The CR750 was produced as a works machine for Honda to demonstrate the advanced performance that the new model was about to bring to the market. The main campaign for doing so was at the Daytona in 1970, where Dick Mann ended up finishing first, other team members (and breakdowns) aside it was an impressive feat. A very iconic part of the Daytona winning bike, and the subsequent CR kit bikes was the twin leading shoe rear brake

This rear hub was cast in magnesium, but that did not make it light!

A company in Italy used to make a replica of the CR rear hubs, which looked very smart in the images I have seen online but were very expensive and are lo longer available. A CR 'guru' in the UK also made a batch around 10 years ago. I was going to make a replica of the rear hub by scaling photographs and begging for measurements however this has never really excited me as it was replicating a replica and would only ever be a tribute rather than a detailed replica part.

Cut a long story short, after some serious looking I found an original part:

Another bit of this jigsaw started.

Also purchased the ignition for the bike so I can start to think about coil and CDI unit lugs:

Although this was expensive, it is nicely made and is rated pretty well.

I think the CR would of had a different hub and a different heat displacement system ? When I have been fitting new liners to the rear hub, I have had quite a few customers ask, if I could also remove the fins as it is in the lathe and I always refuse because I have known a few people do this and had over heating problems. More so with a front drum but, a few with a disc.

I think the CR would of had a different hub and a different heat displacement system ? When I have been fitting new liners to the rear hub, I have had quite a few customers ask, if I could also remove the fins as it is in the lathe and I always refuse because I have known a few people do this and had over heating problems. More so with a front drum but, a few with a disc.

Hi Trigger,

Yes you are correct it was a different part, and was cast in Magnesium but my bike is a replica. I don't think It will be problematic due to the size of the disk, and surface area change, but I will certainly keep an eye on it,

You will need to get info on heat displacement in alloy of that grade, it is totally different than magnesium. You will always see more fins on a rear drum as, it needs to cool the shoes and bearings. The front hub fins will just cool be bearings, no fins means a overheating problem to the bearings.

Heat always transfers to the smaller area with alloy. Think about removing all the engine fins on a air cooled engine, it will overheat I studied this years ago but, can remember all the tech on it and I had a look around last night for the study and data paperwork but, it must of been binned when I moved.

You will need to get info on heat displacement in alloy of that grade, it is totally different than magnesium. You will always see more fins on a rear drum as, it needs to cool the shoes and bearings. The front hub fins will just cool be bearings, no fins means a overheating problem to the bearings.

Heat always transfers to the smaller area with alloy. Think about removing all the engine fins on a air cooled engine, it will overheat I studied this years ago but, can remember all the tech on it and I had a look around last night for the study and data paperwork but, it must of been binned when I moved.

Hi Trigger,

I understand this, as I also studied it and will do some calcs at some point as I have the part drawn up. Before doing the calcs my gut is that as this bike will never be 'raced' and that I have not removed much material/area I will still have a good factor of safety,